The sharply increased cost of locomotive fuel in the past several years has caused increased efforts in the railroad industry to reduce tare weight of rolling stock, since fuel consumption is related to the gross weight of the shipment (train plus cargo). While reduced weight is an important consideration in any type of shipment, it is especially important in piggyback (highway trailer or container carried on a flatcar hereinafter TOFC and COFC, respectively) shipments, where the tare weight of the trailer or container is in addition to the tare weight of the flatcar. This "double tare" weight handicaps the rail mode of transportation in its competitive position, via a vis highway transportation for containerized cargo, even though the latter is generally considered to be less efficient in its use of fuel.
Piggyback traffic is generally carried on flatcars of 85 to 89 feet in length. These cars can readily handle two trailers or containers 40 feet long; however, in recent years, the 45-foot highway trailer has come into popular use and presently constitutes a large percentage of the total production of highway trailers. Obviously, two 45-foot trailers cannot be carried on an 89-foot flatcar, and it often happens that only one 45-foot trailer is carried on an 89-foot car, thereby further reducing the fuel efficiency of the operation.
The construction of longer cars to accommodate two 45-foot trailers or containers to remedy this problem is impossible because the railroad industry through its industry association, the Association of American Railroads (AAR), has placed a length limit of 89 feet, 4 inches on any cars constructed in the future. This length restriction is necessary because of operating problems inherent in long cars having long end overhang (beyond the railway trucks). Typically, the cars tend to pull off curves in conditions of heavy pull and to jack-knife under heavy buff forces. Additionally, the geometry of long cars causes them to track poorly, and with the long end overhang there is a tendency for the air hose connections between cars to separate in operation and cause an emergency application of the train air brakes. Still further, long cars must be made quite heavy in order to support the carried weight which is concentrated at the center of the car where the adjacent ends of the two containers or trailers are supported, thereby adding further construction expense and burdens to the pulling equipment.
Accordingly, one object of the present invention is to improve the efficiency of piggyback equipment by providing a unique railway car assembly having the ability to transport a number of trailers or containers less expensively than heretofore possible.
Another object of the invention is to provide railway car assembly which may economically and easily carry variously sized trailers or containers.
Another object of the invention is to provide a railway car assembly having improved overall operating characteristics.
Another object of the invention is to provide a more streamlined piggyback railway car assembly which reduces potential lading damage and pilferage.
Still further, another object of the invention is to provide a basic railway car which is less expensive to build, less costly to maintain and will cost less to operate.